Ahh, college t-shirt rivalries. There was a shirt that was banned on campus where I went to school (Luther), our big rivals were Wartburg, affectionately called the Warts or Hogs, stuff like that. The shirt said something like "Luther vs. Wartburg: Anyway you look at it, Wartburg's screwed" And had a bunch of drawings of a Luther guy having sex with a Wartburg cheerleader in various positions. Stuff like that doesn't go over too well at a small private college. Damn, I can't think of any other good ones off the top of my head.
My wife went to a school (in the same conference) whose nickname was the Beavers. There's another school in the conference called the Peacocks. You can imagine the stuff they came up with for that one when they played. "Beat UIU so the 'Cocks never rise again"